Revert "Fix for 12837: Duration's get and individual unit getters are bug-prone.

This reverts commit 3508ce56c3c299709f747e59bdfcace03dd6f30c.

Okay, since Martin merged this so quickly without discussion, and Steven
seems to feel very strongly about needing to discuss it further, I'm
reverting this commit and will then open a new pull request for it.